1. Field of the Invention
The present invention relates to a mounting structure of a dust cover in a hydraulic shock absorber such as a front fork of a motor cycle or the like, and a manufacturing method of the dust cover.
2. Description of the Related Art
In a dust cover of a front fork in a motor cycle or the like, an exterior appearance is improved by applying an ornamental chrome plating to a steel plate or the like, for improvement of commodity and saleability properties.
In a dust cover 160 in Japanese Patent Application Laid-Open No. 11-51106, a cylindrical cover main body 165 and a cup-shaped flange 164 are separately formed as shown in FIGS. 5A and 5B. The flange 164 is obtained by drawing a ring-shaped steel plate blank, and is constituted by a short cylinder portion 164a and a flange portion 164b continuously provided in an inner diameter side of the short cylinder portion 164a. The dust cover 160 is structured by fitting and inserting an end portion of the cover main body 165 to an outer periphery of the short cylinder portion 164a in the flange 164 and connecting them by applying a spot welding to four circumferential portions in the fitted and inserted portion. The flange 164 is made of a thicker steel plate than that of the steel plate of the cover main body 165, thereby ensuring a strength of the flange portion 164b. 
The prior art has the following problems.
(1) It is hard to maintain a flatness in a top surface portion 178 of the flange portion 164b in the dust cover 160. There is a risk that the dust cover 160 falls down on to incline when bringing the flange portion 164b into contact with a lower surface of a mounting bracket, whereby an opening of the cover main body 165 of the dust cover 160 is in contact with an outer peripheral surface of a cylinder member. The flatness in the top surface portion 178 of the flange portion 164b is not secured because it is hard to maintain a roundness (a radius of circle) in a crossing portion R between the short cylinder portion 164a and the flange portion 164b when drawing the flange 164. A crossing angle of the flange portion 164b with respect to the short cylinder portion 164a becomes an obtuse angle, whereby the top surface portion 178 of the flange portion 164b is open to an outer side in an axial direction. Further, another reason is that the roundness (the radius of circle) is generated in the periphery of a center hole of the top surface portion 178 in the flange portion 164b due to a press roll over (a burr in an opposite side) generated in a side of a blanking surface at a time of blanking the center hole of the top surface portion 178 in the flange portion 164b, the width itself of the flange portion 164b is comparatively small, and a comparatively large roundness (a radius of circle) exists in an outer peripheral side of the flange portion 164b, and the like.
(2) It is difficult to secure an angularity of the flange portion 164b with respect to the center axis of the cover main body 165 when welding the cover main body 165 to the flange 164, and there is a risk that a welding distortion between the flange 164 and the cover main body 165 distorts the flatness in the top surface portion 178 of the flange portion 164b. 
(3) A welding trace between the flange 164 and the cover main body 165 is generated after chrome plating the dust cover, so that the exterior appearance commodity and saleability properties are lowered.
(4) Since the dust cover is constituted by the flange 164 and the cover main body 165, the control cost for preparing parts and the like is increased, in addition that welding is required, whereby cost is increased.